I would not QT
a Mandarine because they live off pods
. I would put her in the main tank straight away. I have one, she had no problems.
I saw some spots on her that I thought were ick, but it turned out to be sand. If you see white spots, its most likely just sand. As a shovel head, they tend to get sand on their bodies and the slime coat helps it to stick.
Edit: Also if you are really worried about ick, just mix some garlic into your fish food (let is soak before feeding). It is a natural ick fighter. Something about ick does not like the way it smells when the fish eat it.